linux-kernel - Re: [PATCH 0/2] iommu/vt-d: Fix lockdep splat in intel_iommu

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Date:   Fri, 30 Sep 2022 10:23:10 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Joerg Roedel <joro@...tes.org>, Kevin Tian <kevin.tian@...el.com>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] iommu/vt-d: Fix lockdep splat in intel_iommu_init()

On 9/27/22 1:31 PM, Lu Baolu wrote:
> Hi folks,
> 
> As commit c919739ce472 ("iommu/vt-d: Handle race between registration
> and device probe") highlights, a lockdep splat issue happens after
> moving iommu probing device process into iommu_device_register().
> 
> This is due to a conflict that get_resv_regions wants hold the
> dmar_global_lock, but it's also possible to be called from within a
> section where intel_iommu_init() already holds the lock.
> 
> Historically, before commit 5f64ce5411b46 ("iommu/vt-d: Duplicate
> iommu_resv_region objects per device list"), the rcu_lock is used in
> get_resv_regions. This commit converted it to dmar_global_lock in order
> to allowing sleeping in iommu_alloc_resv_region().
> 
> This aims to fix the lockdep issue by making iommu_alloc_resv_region()
> available in critical section and rolling dmar_global_lock back to rcu
> lock in get_resv_regions of the Intel IOMMU driver.

A gentle ping. Any comments to this fix? It's better to work out a
feasible solution before the users keep complaining. :-)

Best regards,
baolu